Go to the page of the Express Form you'd like to change. Change it's template to “Express Form Templating Handles”. This template will add extra class to your grouped elements. Here's an example of the opening HTML tag/element:
<div class=”form-group ak-handle-title at-handle-text”>
As you can see, it adds "ak-handle-title", as this is a "Title" field (ak = attribute key) and "at-handle-text" as this is a text type (attribute type). This way, you could perhaps make this form element 50% of the container, and float it to the left instead of being a 100% element. Like so (CSS code):
And of course float other elements too, do some clears and make it all responsive. This way you don’t need to add in a grid and have tons of different templates. Just use one and style your CSS accordingly. The CSS is something you’d have to write yourself of course. It’s not provided by the Add-On, because each and every site uses a different framework, different CSS et cetera. Should be best to include CSS into your main .css (or .less) file (of the theme) and keep the data as low as possible.